1. 1 Chapter 15 Network Properties (Ownership, Service Paradigm, Measures of Performance)

2. 2 Network Ownership And Service Type  Private  Owned by individual or corporation  Restricted to owner’s use  Typically used by large corporations  Public  Owned by a common carrier  Individuals or corporations can subscribe  “Public” refers to availability, not data

3. 3 Advantages and Disadvantages  Private  Complete control  Installation and operation costs  Public  No need for staff to install/operate network  Dependency on carrier  Subscription fee

4. 4 Public Network Connections  One connection per subscriber  Typical for small corporation or individual  Communicate with another subscriber  Multiple connections per subscriber  Typical for large, multi-site corporation  Communicate among multiple sites as well as with another subscriber

5. 5 Virtual Private Network  A service  Provided over public network  Interconnects sites of single corporation  Acts like private network  No packets sent to other subscribers  No packets received from other subscribers  Data encrypted

6. 6 Virtual Private Network

7. 7 Network Service Paradigm  Fundamental characteristic of network  Understood by hardware  Visible to applications  Two basic types of networks  Connectionless  Connection-oriented

8. 8 Connectionless ( CL )  Sender  Forms packet to be sent  Places address of intended recipient in packet  Transfers packet to network for delivery  Network  Uses destination address to forward packet  Delivers

9. 9 Characteristics of Connectionless Networks  Packet contains identification of destination  Each packet handled independently  No setup required before transmitting data  No cleanup required after sending data  Think of postcards

10. 10 Connection-Oriented (CO)  Sender  Requests “connection” to receiver  Waits for network to form connection  Leaves connection in place while sending data  Terminates connection when no longer needed

11. 11 Connection-Oriented (CO) (continued)  Network  Receives connection request  Forms path to specified destination and informs sender  Transfers data across connection  Removes connection when sender requests  Think of telephone calls

12. 12 Terminology  In conventional telephone system  Circuit  In CO data network  Virtual Circuit  Virtual Channel

13. 13 Comparison of CO and CL  CO  More intelligence in network  Can reserve bandwidth  Connection setup overhead  State in packet switches  Well-suited to real-time applications  CL  Less overhead  Permits asynchronous use  Allows broadcast / multicast

14. 14 Two Connection Types  Permanent Virtual Circuit (PVC)  Entered manually  Survives reboot  Usually persists for months  Switched Virtual Circuit (SVC)  Requested dynamically  Initiated by application  Terminated when application exits

15. 15 Examples of Service Paradigm Various Technologies Use

16. 16 Connection Multiplexing  Typical computer has one physical connection to network  All logical connections multiplexed over physical interconnection  Data transferred must include connection identifier

17. 17 Connection Identifier  Integer value  One per active VC  Not an address  Allows multiplexing  Computer supplies when sending data  Network supplies when delivering data

18. 18 Example Connection Identifier (ATM)  24 bits long (The full address is 160 bits)  Divided into two parts  Virtual Path Identifier  Virtual Channel Identifier  Known as (VPI/VCI)  Different at each end of connection  Mapped by switches

19. 19 Illustration of ATM VC  Switch maps VPI/VCIs  17 to 12  96 to 8

20. 20 Two Primary Performance Measures  Delay  Throughput

21. 21 Delay  Time required for one bit to travel through the network  Three types (causes)  Propagation delay  Switching delay  Queuing Delay  Intuition: “length” of the pipe

22. 22 Throughput  Number of bits per second that can be transmitted  Capacity  Intuition: “width” of the pipe

23. 23 Components of Delay  Fixed (nearly constant)  Propagation delay  Switching delay  Variable  Queuing delay  Depends on throughput If delay is changing rapidly, we refer to it as Jitter

24. 24 Relationship Between Delay and Throughput  When network idle  Queuing delay is zero  As load on network increases  Queuing delay rises  Load defined as ration of throughput to capacity  Called utilization

25. 25  Define  D 0 to be the propagation and switching delay  U to be the utilization (0  U  1)  D to be the total delay  Then  High utilization known as congestion Relationship Between Delay and Utilization

26. 26 Practical Consequence Any network that operates with a utilization approaching 100% of capacity is doomed

27. 27 Delay-Throughput Product  Delay  Time to cross network  Measured in seconds  Throughput  Capacity  Measured in bits per second  Delay * Throughput  Measured in bits  Gives quantity of data “in transit”

28. 28 Summary  Network can be  Public  Private  Virtual Private Network  Uses public network  Connects set of private sites  Addressing and routing guarantee isolation

29. 29 Summary (continued)  Networks are  Connectionless  Connection-oriented  Connection types  Permanent Virtual Circuit  Switched Virtual Circuit  Two performance measures  Delay  Throughput

30. 30 Summary (continued)  Delay and throughput interact  Queuing delay increases as utilization increases  Delay * Throughput  Measured in bits  Gives total data “in transit”